package org.xiaojinlong.thread;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.*;

/**
 * @author Jin Long
 *         2015/10/18
 */
public class HorseRace {
    private static class Horse implements Runnable {
        private static int counter;
        private final int id = counter++;
        private int strides;
        private static Random rand = new Random(47);
        private static CyclicBarrier barrier;

        public Horse(CyclicBarrier b) {
            barrier = b;
        }

        public synchronized int getStrides() {
            return strides;
        }

        @Override
        public void run() {
            try {
                while (!Thread.interrupted()) {
                    synchronized (this) {
                        strides += rand.nextInt(3);
                    }
                    barrier.await();
                }
            } catch (InterruptedException e) {
                // a legitimate way to exit
            } catch (BrokenBarrierException e) {
                // This one we want to know about
                throw new RuntimeException(e);
            }
        }

        @Override
        public String toString() {
            return "Horse " + id + " ";
        }

        public String tracks() {
            StringBuilder s = new StringBuilder();
            for (int i = 0; i < getStrides(); i++)
                s.append("*");
            s.append(id);
            return s.toString();
        }
    }

    static final int FINISH_LINE = 75;
    private List<Horse> horses = new ArrayList<>();
    private ExecutorService exec = Executors.newCachedThreadPool();

    public HorseRace(int nHorses, final int pause) {
        CyclicBarrier barrier = new CyclicBarrier(nHorses, new Runnable() {
            @Override
            public void run() {
                StringBuilder s = new StringBuilder();
                for (int i = 0; i < FINISH_LINE; i++)
                    s.append("=");
                System.out.println(s);
                for (Horse horse : horses)
                    System.out.println(horse.tracks());
                for (Horse horse : horses) {
                    if (horse.getStrides() >= FINISH_LINE) {
                        System.out.println(horse + "won!");
                        exec.shutdownNow();
                        return;
                    }
                }
                try {
                    TimeUnit.MILLISECONDS.sleep(pause);
                } catch (InterruptedException e) {
                    System.out.print("barrier-action sleep interrupted");
                }
            }
        });

        for (int i = 0; i < nHorses; i++) {
            Horse horse = new Horse(barrier);
            horses.add(horse);
            exec.execute(horse);
        }
    }

    public static void main(String[] args) {
        int nHorses = 7;
        int pause = 200;
        new HorseRace(nHorses, pause);
    }
}
